This invention relates to the polymerization of glucose and other monosaccharides using mineral acids such as low levels of phosphoric acid to yield edible materials particularly suitable for food use.
With increased consumer demand for healthy, reduced-calorie food products, polymerized carbohydrate materials such as polydextrose have gained popularity in recent years as substitutes for conventional sweeteners, flour, and other starches in recipes, and as fat-sparing agents. Reduction of caloric density in food products using polydextrose, for example, can be significant because polydextrose delivers only about 1 kcal/gram, which is about 25% the value of glucose and 9% the value of fat (Figdor, S. K., and Bianchine, J. R., J. Agric. Food Chem. 1983, 31: 389-393). Yet polydextrose is a bland-tasting bulking agent that can add the mouthfeel, texture, and palatability of higher calorie carbohydrates to food without affecting the utilization of vitamins, minerals or essential amino acids that has plagued the use of some other sugar and fat replacers. In addition, in dental tests, polydextrose does not promote tooth decay or plaque formation, so it can be used in reduced-cariogenic confectioneries and the like. Use of polydextrose and related polysaccharides in food products to totally or partially replace higher calorie ingredients, and to augment artificial sweeteners replacing sugars, permit a dietetic food to retain its appetizing physical appearance, while contributing to the texture and eating quality of the food. (For a review of polydextrose, see Murray, P. R., in Birch, G. G., and Lindley, M. G., eds., Low-Calorie Products, Elsevier Applied Science, New York, 1988, chapter 7, pages 84-100.)
Water-soluble, highly branched polydextrose is now widely used as a bulking agent, formulation aid, humectant, and texturizer in frozen dairy compositions such as ice cream, ice milk, and other desserts; in baked goods such as cakes, cookies and pastries containing flour, and in baking mixes; and in icings, candy, syrups, toppings, sauces, gelatins, puddings, beverages, and chewing gum.
Glucose is known to polymerize under acidic catalysis. Mora, for example, described the preparation of branched-chain carbohydrate polymers in U.S. Pat. No. 2,719,179. His process involved holding a saccharide or a mixture of saccharides in an inert solvent or diluent in the presence of a Lewis acid catalyst at a temperature of xe2x88x9280xc2x0 C. to 110xc2x0 C. He suggested that hydrochloric acid, phosphoric acid, phosphorous acid, sulfuric acid, aluminum chloride, zinc chloride, stannic chloride, boron trifluoride, antimony trichloride, or p-toluene sulfonic acid might be useful for the practice of his invention, although his examples employ only hydrochloric acid to polymerize dextrose.
Under acidic conditions at elevated temperatures, carbohydrates, especially monosaccharides, are vulnerable to a variety of reactions, including hydrolysis, dehydration, decomposition, and polymerization. Products, which tend to have yellow to brown colors and caramel-like odors, are complex mixtures of anhydro sugars, hydroxymethyl furfural and other furan compounds, levulinic acid, formic acid, soluble brown polymers, and insoluble humins. These reactions are described, for example, in W. Pigman, The Carbohydrates, Chemistry, Biochemistry, and Physiology (Academic Press, New York, 1957, pages 57 to 60); in W. Pigman and D. Horton, The Carbohydrates, Chemistry and Biochemistry (Academic Press, New York, 1972, volume IA, pages 175 to 186, and volume IIA, page 95); in O. R. Fennema, Food Chemistry (2nd ed., Marcel Dekker, Inc., New York, 1985, page 98); and in B. F. M. Kuster, Volume 42 of Starch/Starke (1990, pages 314-321). The reactions are difficult to control during acid-catalyzed polymerization of saccharides, where the object is a polymer having bland taste and low color.
In U.S. Pat. No. 2,436,967, Leuck described a series of experiments comparing catalysts or combinations of catalysts for the polymerization of sugars, preferably in a molten state. He found that alkaline salts could not be effectively used because they had a tendency to break down or destroy the dextrose, and that neutral salts were more effective than an acid as a catalyst for polymerization. He reported that, as a general rule, neutral salts gave larger amounts and higher degrees of polymerization than acids or acid salts, and have a further advantage in that they do not bring about as much color formation per unit of time or per unit of temperature as do acids or acid salts.
Rennhard reviewed the disadvantages of using mineral acid to promote polymerization of sugars to produce edible products in U.S. Pat. Nos. 3,766,165 and 3,876,794. Polysaccharides made from their constituent mono- or disaccharides using these acid catalysts were typically dark-colored and off-flavored. In addition to the caramelization and/or browning observed, mineral acids tend to catalyze the reverse reaction, depolymerization, forming acid reversion products that cut down on the efficiency of the forward reaction. Moreover, for food use, inedible catalysts, solvents and the like used in the preparatory procedures must be substantially completely removed from the products formed in the polymerization, and in some cases this was not possible as, for example, where the catalysts formed complexes with the products. Although a more recent publication suggested that hydrochloric acid may be desirable for condensing glucose under some circumstances (U.S. Pat. No. 4,965,354 to Yanaki and Muebuta), the patent did not disclose preparations incorporating a polyol with a saccharide in the polymerization mixture, or, as evidenced by enzymatic degradation studies (Table 6, column 9), formation of highly branched polydextrose for food applications.
Rennhard proposed that mineral acids be replaced with non-volatile, edible organic polycarboxylic acids for the manufacture of polysaccharides for food use (Mn, from 1500 to 18,000). He tested a variety of these acids as catalysts and cross-linking agents for the polymerization of glucose and maltose and found that he could obtain good products if the reaction were carried out in a melt at reduced pressure. He found that superior products could be obtained if he included a food acceptable polyol such as sorbitol in the saccharide-carboxylic acid reaction mixture prior to polycondensation. In addition, he reported that, by adjustment of the initial acid concentration, the reaction duration, and reaction temperature, two classes of polyglucose and polymaltose, soluble and insoluble, could be obtained simultaneously or separately.
Rennhard""s use of food grade citric acid to make polydextrose eventually became a process identified by the Food and Drug Administration as safe (21 C.F.R. xc2xa7172.841). Subsequent publications centered around ways of improving the product of the reaction. Rennhard""s polydextrose possessed a slightly bitter taste which limited its utility in foods, so many disclosures were directed toward taste improvement. In U.S. Pat. No. 4,622,233 to Torres, for example, anhydroglucose (thought to contribute to the bitter taste), other impurities, and some color were removed from the polydextrose by treatment with a solvent and a food-approved bleaching agent. U.S. Pat. Nos. 4,948,596 and 4,956,458 to Bunick, et al., and Luo, et al., respectively disclosed purification of polydextrose by solvent extraction and reverse osmosis. EP-A-0380248, Guzek, et al., disclosed purifying polydextrose (Mn, from 1500 to 18,000) employing an ion exchange process for removing bound citric acid down to levels of 0.01 to 0.3 mole %. In U.S. Pat. Nos. 5,645,647 and 5,667,593, Guzek, et al., polydextrose was treated by ion exchange to make it substantially free of bitter-tasting residual compounds. A polydextrose having improved color, flavor, and decreased reactivity toward food ingredients having an amine functionality was prepared by hydrogenating the polymer product to remove reducing glucose groups (WO 92/14761 to Borden, et al.).
In U.S. Pat. No. 5,051,500, Elmore discloses the use of carboxylic acid catalysts with small amounts of an inorganic acid as a promoter.
All of the above-mentioned publications are incorporated by reference herein for all purposes as if fully set forth.
Because consumer interest in reduced- and low-calorie food and beverage products is growing, it would be desirable to have alternate processes for economically producing food grade polydextrose using other procedures.
It is an object of the invention to provide another process for the preparation of food grade polysaccharides.
It is a more specific object of the invention to provide a process for the production of edible polysaccharides using selected mineral acids, or a combination of mineral acids and organic acids, particularly in amounts and under conditions required to achieve a selected effect as set forth below.
It is a further object of the invention to provide a process for the production of edible polysaccharides, and particularly polydextrose, using very low levels of phosphoric acid.
It is an additional object of the invention to provide processes for modifying polydextrose and other polysaccharides prepared using certain mineral acid catalysis.
These and other objects are achieved by the present invention which provides a process for preparing highly branched polysaccharides by reacting a saccharide such as maltose, glucose, or other simple sugar, or a glucose-containing material such as hydrolyzed starch in the presence of a polyol such as sorbitol, glycerol, erythritol, xylitol, mannitol, galactitol, or mixtures thereof, typically at a level of from about 5 wt % to about 20 wt % polyol, in the presence of a sufficient amount of one or more mineral acid catalysts, or a mixture of a mineral acid catalyst and an organic acid, to form a polysaccharide suitable for food use, i.e., exhibiting low color and a low level of off-flavors.
Weight percent (wt %), for the purposes of the present specification, is based on the total weight of the polyol, saccharide and catalyst reactants.
In a first embodiment, the process of the invention utilizes very low amounts, preferably from about 0.0001 wt % to about 0.3 wt %, more preferably 0.1 wt % or less, still more preferably from about 0.000 wt % to 0.1 wt %, and especially from about 0.0002 wt % to about 0.06 wt %, of a catalyst component comprising one or more mineral acids selected from hydrochloric acid, sulfuric acid, sulfurous acid, thiosulfuric acid, dithionic acid, pyrosulfuric acid, selenic acid, selenious acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, polyphosphoric acid, hypophosphoric acid, boric acid, perchloric acid, hypochlorous acid, hydrobromic acid, hydriodic acid and silicic acid; acidic alkali metal or alkaline earth metal salts of the above acids such as sodium bisulfate and sodium bisulfite; or mixtures of these acids (and/or acidic akali or alkaline earth metals salts) with phosphoric acid.
In a second embodiment, the process of the invention utilizes very low amounts, preferably from about 0.001 wt % to about 0.09 wt %, more preferably from about 0.006 wt % to about 0.09 wt %, and still more preferably from about 0.01 wt % to about 0.06 wt %, of a phosphoric acid catalyst optionally in combination with a polycarboxylic acid such as citric acid.
In a third embodiment, the process of the invention utilizes, in the catalyst component, a bleaching mineral acid in an amount and under conditions effective to reduce the color and/or off-flavor formation in the resulting polysaccharide. As examples of bleaching mineral acids are some of the above-mentioned mineral acids including sulfurous acid, selenious acid, perchloric acid, hypophosphorous acid and hypochlorous acid, as well as the acidic alkali metal and alkaline earth metal salts thereof such as sodium bisulfite. Typically, such bleaching mineral acids are used in amounts up to about 5.0 wt %, and more preferably up to about 1.0 wt %, as required to achieve the desired effect. Combinations of such bleaching mineral acids with other acid catalysts (including other mineral and/or polycarboxylic acid catalysts) are also part of this third embodiment.
In a fourth embodiment, the process of the invention utilizes, in the catalyst component, a metal chelating mineral acid in an amount and under conditions effective to reduce color and/or off-flavor formation in the resulting polysaccharide due to the presence of metal contaminants. As examples of metal chelating mineral acids are some of the above-mentioned mineral acids including polyphosphoric acid and pyrophosphoric acid, as well as the acidic alkali metal and alkaline earth metal salts thereof. Typically, such metal chelating mineral acids are used in amounts up to about 1.0 wt %, and more preferably up to about 0.5 wt %, as required to achieve the desired effect. Combinations of such metal chelating mineral acids with other acid catalysts (including other mineral and/or polycarboxylic acid catalysts) are also part of this fourth embodiment.
The product so formed by any of the above processes may be neutralized, further purified by ion exchange, size exclusion chromatography, membrane filtration, enzyme treatment and/or carbon treatment, and/or modified by hydrogenation. In some embodiments, the ion exchange purification step involves treatment with an anion exchange or mixed-bed resins.